• Korean Journal of Ornithology
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• v.25 no.2
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• pp.69-76
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• 2018

Sexual dimorphism in birds refers to male-female differences in body size, plumage, color and/or behavior. In general, many seabirds, including the family of Laridae, are monomorphic in plumage-color, which makes the determination of sex difficult in the field because both parents also tend to share a great portion of parental care. The development of an inexpensive sexing tool facilitates understanding the degree of sex-specific parental care in the evolution of the life history. Here, we developed a non-invasive method for the determination of sex using the bill-head morphometric of known captive pairs and applied this tool to wild pairs to document factors underlying male-female parental care during the incubation period of Saunders's gulls (Saundersilarus saundersi). Males exhibited relatively larger bill-head ratios than their mates within naturally formed pairs in captivity, resulting in the determination of sex in12 wild pairs at the nest during the incubation period. Males and females equally shared the incubation role during the daytime, attending the nest at a high rate of 95%. However, the male's proportion of nest attentiveness greatly increased with time towards sunset, presumably reflecting the male duty for nighttime incubation. The present study provides a non-invasive method for the determination of sex in a monomorphic seagull species and highlights how male-female incubation behavior is associated with time of the day, rather than other ecological conditions.

• Korean Journal of Environmental Biology
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• v.28 no.2
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• pp.49-55
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• 2010

There are only 10,000 Saunders' Gull's (Larus saundersi Swinhoe) surviving in the world today. But they are being threatened by coastal habitat, degradation, development pressure and disturbance by humans. Their first breeding record in Korea was in 1998 and the breeding status has been studied, however, the breeding status is not sufficient for this species. This study was performed from May 1999 to June 2009 to clarify breeding populations and trend of the Saunders' Gull population in Korea. The results indicate that the breeding population has been increasing gradually from 300 to 1,300 individuals, though disturbance increased. As threats to the breeding birds, physical environmental factors such as development and human disturbance were identified as a major threatening factors. Also, as a secondary factor, eggs and chicks are falling pray to predators. Incheon bay breeding places have been created by a landfill projects for the purpose of urban and industrial development, thus, these places will no longer be available for this species. In addition, the breeding habitat has been reduced and changed by expansions of development on the ground. Therefore, well planed management schemes should be provided for the species' breeding population to be continually breed and survive.

• Ocean and Polar Research
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• v.31 no.3
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• pp.277-282
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• 2009

Saunders' gulls (Laurs saundersi) which are listed as globally vulnerable species on the IUCN Red List are distributed in East Asia and breed mainly in China and Korea. Their population is estimated to be between 7,100 to 9,600. Songdo reclaimed lands in the western coast of South Korea are the main breeding sites for these species. However, most of these breeding sites have been seriously disturbed in the last several years because of new urban development constructions. This study was conducted to provide baseline data on the breeding ecology of Saunders' gulls. Since 1998, the breeding population has rapidly increased in South Korea, with the number of nests rising from 85 nests in 2000 to 185 nests in 2005. Egg volume is more variable than breadth or length. Clutch size, hatching and breeding success were $2.9{\pm}0.81$ (n=182, mean$\pm$sd.), 48.07% (75 hatched egg/156 eggs) and 29.08% (155 fledglings/533 eggs), respectively. Factors affecting breeding failure were predation, rainfall, starvation and supernormal clutches. These results are provided along with other cited literature to argue for conservation of Saunders' gulls.

• Journal of Wetlands Research
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• v.6 no.1
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• pp.73-87
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• 2004

This study was carried out on Sihwa reclaimed area from January to December in 2003. We observed total 169,351 individuals of 70 species(22 species of waders, 9 species of egrets and 5 species of gulls). Waterbird population was the largest in March(95,465 individuals) and was the smallest from April to June(less than 7,000 individuals). The most dominant species was Pintail(Anas acuta: 58,627 individuals, 34.6%) and other species were Mallards(Anas platyrhynchos: 24.5%), Common Pochards(Aythya ferina: 13.8%), Black-tailed Gulls(Larus crassirostris: 6.1%), Spotbill Ducks(Anas poecilorhyncha: 5.0%) and Greater Scaups(Aythya marila: 2.69%). Sihwa reclaimed area supported many kinds of protected species such as Chinese egrets(Egretta eulophotes), Black-faced Spoonbills(Platalea minor), Eurasian Spoonbills(Platalea leucorodia), Mute Swans(Cygnus olor), Whooper Swans(Cygnus cygnus), and Eurasian Oystercatchers(Haematopus ostralegus). They foraged at waterside of Sihwa lake and rested at reclaimed area. Particularly, Eurasian Oystercatchers bred in habitats with Salicornia herbacea and Suaeda japonica. Reclamation of mud flats and construction of roads, transmission towers and tide embankments disturbed waterbirds in breeding and foraging. We suggest that waterbirds are protected in different action plans according to their status such as breeding, passaging and wintering birds. Maintaining of waterside and swamps in Sihwa reclaimed area will be useful for breeding waterbirds. It is needed to make a protect zone for ecological connecting belt from Oeji isarea, Hyeong isarea, Eum isarea to upper channel on Sihwa lake.